The present invention relates to endoscope light source units and endoscopy systems allowing an endoscope to be applied in an endoscopic diagnosis to two types of inspection, namely, the inspection with a special light in which a mucosal tissue of the living body is illuminated with light in a specified, narrow wavelength band to obtain information on the tissue at a desired depth, and a normal inspection using visible light for illumination.
An endoscopy instrument used for a conventional endoscopic diagnosis performs a normal inspection, whereupon visible light, such as white light, from a light source unit for an endoscope is guided through a light guide, then emitted through an illumination window at the tip of an insertion section of the endoscope so as to illuminate a target site for inspection, and inspect the target site.
Recently employed for endoscopic diagnosis is an endoscopy instrument capable of performing not only the above normal inspection using white light for illumination but the inspection with a special light in which a biological tissue, such as a mucosal tissue of a body cavity wall, is illuminated with light in a specified wavelength band narrower than the wavelength band of white light (hereafter referred to as “narrow-band light”) to obtain information on the biological tissue at a desired depth.
It is readily possible on such an endoscopy instrument as above to visualize biological information unobtainable from conventional inspection images, such as the microstructure of neovascularity occurring in a mucosal layer or submucosa, and the exaggeration of a lesion. If a carcinomatous lesion site is to be inspected, for instance, states of microvessels or microstructures in a superficial layer of a mucosal tissue are observed in more detail by illuminating the tissue with a narrow-band blue light, leading to a more accurate diagnosis of the lesion.
An endoscopy instrument performing inspection not with a narrow-band light but fluorescence as a special light is also employed. In an inspection with fluorescence, a body cavity wall is illuminated with an excitation light to excite a biological tissue, and the variation in intensity of autofluorescence generated by the tissue as excited is utilized to make an earlier finding of a carcinomatous lesion site.
An endoscope light source unit for use in endoscopy instruments performing inspection with fluorescence is disclosed in JP 2005-342033 A and JP 2005-342034 A.
The endoscope light source units as disclosed in JP 2005-342033 A and JP 2005-342034 A each have a white light source emitting white light as visible light, and a semiconductor laser as an excitation light source emitting the excitation light which is light at a shorter wavelength in an ultraviolet region. The optical path from the white light source to the light guide into which the white light is caused to enter is linearly arranged, while the optical path for the excitation light is arranged orthogonally to the optical path for the white light, with the two optical paths being combined together by a dichroic mirror as an optical path-combining element.
In the disclosed units, dichroic mirrors are characterized in that they transmit light at a wavelength equal to or longer than a specified one, and reflect light at a wavelength shorter than the specified one, that is to say, transmit a large proportion of the white light, and reflect the excitation light.
In the inspection with a narrow-band light as described above, a biological tissue is illuminated with only two narrow-band lights, namely, a narrow-band blue light suitable for the inspection of a superficial tissue layer and a narrow-band green light suitable for the inspection of intermediate and superficial tissue layers, without using a narrow-band red light chiefly suitable for the inspection of intermediate and deep layers of a biological tissue, in order to facilitate the inspection of microvessels or microstructures in a superficial layer of the biological tissue. In other words, required for the inspection are only the blue image signals (narrow-band blue light data) obtained by an imaging sensor as a result of the illumination with the narrow-band blue light that chiefly contain information on a superficial tissue layer, and the green image signals (narrow-band green light data) obtained by an imaging sensor as a result of the illumination with the narrow-band green light that chiefly contain information on intermediate and superficial tissue layers. With the green image signals being allocated to the red image data of a color image, and the blue image signals to the green and blue image data, a pseudo-color image composed of 3-ch (three-channel) color image data is produced, and displayed on a monitor, for instance (see JP 4009626 B).
In the technology as disclosed in JP 4009626 B, the two narrow-band lights used for the inspection with a narrow-band light, the narrow-band blue light and the narrow-band green light, are emitted frame-sequentially by using a color filter to switch, in a time-sharing manner, the light from a white light source to be used for the inspection with a normal light. In this connection, in the inspection with a normal light also, light from a white light source is switched by means of a color filter in a time-sharing manner to frame-sequentially emit red, green, and blue lights.
In the endoscope light source units as disclosed in JP 2005-342033 A and JP 2005-342034 A, both adapted for the inspection with autofluorescence as a special light, the excitation light to be used is light at a shorter wavelength in an ultraviolet region and, accordingly, a light component within a specified wavelength range in the visible spectral region of the white light will not be lost when the white light and the excitation light are combined together by the dichroic mirror. On the other hand, in the endoscope light source unit adapted for the inspection with a narrow-band light in a visible spectral region as a special light, to which the technology as disclosed in JP 2005-342033 A and JP 2005-342034 A is applied, white light and the narrow-band light are combined together by a dichroic mirror. Consequently, light in the same wavelength band as the narrow-band light will be lost from the white light which is emitted from the endoscope light source unit when the source of the narrow-band light is switched off.
In other words, if a normal inspection is conducted using an endoscope provided with such an endoscope light source unit as above, the light quantity of white light is considerably reduced in the wavelength band to which a narrow-band light is attributed (specified wavelength range). As a result, an image of the object to be imaged or inspected is obtained as much reduced in accuracy than usual and rendered darker as a whole, which may cause a false diagnosis, such as overlooking of a lesion.
In addition, in the technology as disclosed in JP 4009626 B, the narrow-band lights used for the inspection with a special light are each light in a wavelength band narrower than that of the white light (including RGB lights) emitted during the normal inspection, so that the output light quantity of a narrow-band light source is reduced as compared with that of a white light source, thus rendering an image displayed on a monitor darker as a whole than that displayed during the normal inspection.
If, during the inspection with a special light as described in the reference, the output from the narrow-band light source in itself is raised, that is to say, the output light quantity is increased with respect to narrow-band lights in order that an image displayed on a monitor is made brighter, and light quantity shortages are covered, more heat will be generated at the tip of an endoscope, leading to an unwanted thermal load on the living body as a target for inspection. Such thermal load may not only affect the living body, damage it for instance, but cause the deterioration of the endoscope in itself and, then accordingly, of the endoscopy instrument, with its service life being greatly shortened.
Moreover, it is difficult to apply the technology of JP 2005-342033 A and JP 2005-342034 A to the endoscopy instrument as disclosed in JP 4009626 B because the light quantity of white light is considerably reduced in a specified wavelength range during a normal inspection conducted using an endoscope provided with the light source unit of JP 2005-342033 A or JP 2005-342034 A, as described above.